Many consumer products and other electrical devices need to convert an AC power input provided by electrical mains into a DC power output that is required by the device's circuitry. An external AC power adaptor is often used for such a purpose. In addition to performing its primary function of converting an AC input into a DC output having characteristics suitable for the device's circuitry, an external AC power adaptor provides several design advantages over an internal AC power adaptor.
For example, safety concerns and/or regulations dictate that the power circuitry of an AC power adaptor be housed in an appropriately secure manner to reduce the risk of user injury. Typically, any component that can become energized with AC power needs to have a secure housing that protects against inadvertent user contact with the energized component. By moving such power circuitry outside of a device, the device itself may not need to incorporate the same level of safety features because the device only uses the DC output of the adaptor. In addition, the device may be made smaller and lighter because the size and weight of the AC power adapter, along with its housing or other safety features, is located outside of the device.
An external AC power adaptor is typically located on a device's plug or in a “brick” configuration that may be located along the device's power cord. An example of the latter type of conventional external AC power adaptor is illustrated in FIG. 1. Power circuitry 115 is located within housing 120 of external AC power adapter 100. Power circuitry 115 receives AC power by way of wire 105 and outputs DC power by way of wire 110. As noted above, the presence of energized power circuitry 115 requires enhanced safety precautions. This is especially important for external AC power adaptors in general because such adaptors are typically placed on the floor, behind furniture, etc., under uncontrolled and unobserved conditions. As a result, external AC power adaptor 100 needs to be capable of withstanding a variety of physical stresses, including drops, spills, and so forth. In addition, housing 120 of adaptor 100 needs to be able to isolate any energized components from children, pets and the like that may unknowingly attempt to access such components. Most conventional external AC power adaptor 100 manufacturers have opted to deal with these safety issues by constructing such an adaptor 100 with housing 120 that is a sealed, resilient assembly with no ventilation provided to the interior components to prevent any possibility of contact with any energized components.
Unfortunately, all power supplies, and therefore all external AC power adaptors, generate some amount of interior heat. An external AC power adaptor having a sealed housing does not provide an efficient means for dissipating internal heat, which in turn limits the amount of power that can be economically delivered to a device without overheating the adaptor.
For example, plastic is usually the material used to construct housing 120 because it is a strong, low-cost electrical insulator having a favorable heat-rise allowance as dictated by applicable government agency standards. The interior heat-generating parts of power circuitry 115 must diffuse their heat load through such a plastic housing 120 into what is typically still air. Because plastic is a poor thermal conductor, and because still air results in poor thermal transfer, it can be seen that a conventional external AC power adaptor is severely limited in the amount of power it can supply for a given adaptor 100 size.
Accordingly, there is a need for a means by which an external AC power adaptor can provide an improved cooling mechanism while maintaining the inherent safety and hazard integrity provided by a sealed housing. The present invention satisfies this need.